1. Field of the Invention
This invention relates to isotopic and molecular separation, and in particular provides method and apparatus for generally exciting and selectively de-exciting preselected species preparatory to physical separation.
2. Description of the Prior Art
For many applications it is desirable to separate selected atomic species (isotopes or molecules) from a mixture including the species. Typically the mixture includes species which have substantially similar characteristics and, accordingly, sophisticated forms of differentiation and separation are required.
Among the applications for which such fine separation is required is the production of fissionable isotopes for nuclear reactor utilization. Among the most common examples of isotopic separation is the division of the uranium-235 isotope from other uranium isotopes, particularly uranium-238. In the past the isotopic separation has been based primarily upon slight chemical or mass differences, involving in most cases a complex, costly cascading system, such as a diffusion network, which requires large amounts of input energy.
More recently optical systems have been proposed which utilize selective photoexcitation and/or ionization of the desired isotope or molecule in preference to other species as a basis for differentiation prior to permanent separation. It is generally known that a molecule or atom in an excited state has different physical properties and chemical properties from a similar but unexcited species. These differences form the basis for a number of the proposed methods for separating isotopes. While such systems hold much promise as improvements over mass separation, they are not without deficiences. Most notably, because the differences in mass and electronic levels among related isotopes and vibrational and rotational frequencies among related molecules are quite small, as are the differences in optical wavelengths, a highly monochromatic source is generally required for selective electronic excitation. As a practical matter lasers prove to be the principal source for provision of sufficiently monochromatic radiation with sufficient power to yield useful separation. Consequently, recently proposed systems utilize an external laser to irradiate an isotopic mixture of atoms or molecules. Since the laser must provide a frequency corresponding precisely to the optimum frequency for exciting the desired isotope as opposed to other isotopes in the mixture, tunable lasers must be utilized. Although tunable lasers exist, they are generally inefficient, relatively difficult to use, expensive and of relatively low power. Furthermore, the absorption of the laser radiation by the isotopic or molecular medium can also involve serious losses, further reducing the overall efficiency for selective excitation. Also, because the isotope shift differs in magnitude for the different electronic levels upon which selective photoexcitation is based, it is often difficult to find suitable compounds which combine a usable isotope shift with a physical state, preferably gaseous, suitable for use in separation processes.
It is therefore desirable to further improve upon selective isotope excitation and separation processes, particularly to provide systems of increased efficiency, lower cost, power and complexity, and adaptable to a wider variety of compounds than heretofore obtainable. It is further desirable to provide these beneficial results from individual components and procedures existing in today's technology.